I. Types of miscarriage.
1.Spontaneous abortion
Domestic definition is less than 28 weeks of gestation, fetal weight less than 1000g termination of pregnancy, accounting for about 15% of the miscarriage population, most spontaneous abortions occur before 20-22 weeks.
2.Habitual miscarriage
It refers to 3 or more spontaneous miscarriages, with an incidence of 0.5%~3%, and is more often defined as “recurrent miscarriage”.
3.Recurrent miscarriage
In the past, it refers to more than 3 spontaneous abortions, but now it is reduced to 2 or more because from clinical observation, the etiology of 3 and 2 abortions and the chance of subsequent abortions are similar, and the effect of each abortion will reduce the patient’s chance of getting pregnant again. The etiology of recurrent miscarriage is currently considered to be more complex and difficult to treat. Recurrent miscarriages are classified as primary (meaning that the patient has never had a history of full-term delivery) and secondary (recurrent spontaneous miscarriages that occur subsequently after the patient has had a history of full-term secretion).
4. Biochemical pregnancy
It is a pregnancy in which the blood chorionic gonadotropin is elevated but the gestational sac is not visible on ultrasound. Biochemical pregnancy and spontaneous abortion are sometimes difficult to define. There is controversy as to whether a biochemical pregnancy is a spontaneous or recurrent miscarriage. However, patients who have recurrent biochemical pregnancies should be taken seriously. The chances of chromosomal abnormalities are higher in very early embryo loss like biochemical pregnancy.
Second, the etiology of recurrent miscarriage
1. Embryonic chromosomal abnormalities
Among the miscarried embryos, some of them are caused by embryonic chromosomal abnormalities, of which 53% are early miscarriages and 36% are late miscarriages. The earlier the spontaneous miscarriage such as biochemical pregnancy and early embryo loss, the greater the chance of embryo chromosomal abnormalities. Chromosomal abnormalities in fetuses with normal chromosomes in both spouses are associated with a greater age of the mother at birth. Women’s age has a greater impact on spontaneous abortion, with a higher rate of spontaneous abortion in women aged 22-23, the lowest rate in women aged 25-30, and an increased rate of chromosomal abnormalities in embryos after the age of 30, reaching 35% in women aged 35 and 50% in women aged 40. Now that the second child is open, many women in their 40s need to pay attention to the incidence of such spontaneous abortions.
2, maternal endocrine disorders
(1) Luteal insufficiency
Luteal insufficiency can cause poor meconium response in pregnancy and affect the implantation of pregnant eggs. There is no gold standard for the diagnosis of luteal insufficiency. Luteal insufficiency is present in a proportion of patients with recurrent miscarriage. Patients with endometriosis often have a combination of follicular luteinization, which is due to abnormal luteinizing hormone production, or early onset of ovulation of small follicles, or insufficient support for final follicular maturation and ovulation.
Blood progesterone levels are pulsatile and very volatile and are not recommended to be used as an indicator of pregnancy progression.
(2) Polycystic ovary syndrome
Polycystic ovary syndrome leads to a decrease in egg quality and endometrial tolerance. In addition, hyperandrogenemia and hyperinsulinemia in polycystic ovary syndrome are harmful to pregnancy. Some patients with polycystic ovary syndrome combined with antiphospholipid syndrome are prone to thrombosis, which is detrimental to fetal blood supply and prone to miscarriage, and require intensive anticoagulation therapy.
(3) Hyperprolactinemia
It can lead to luteal insufficiency, decreased egg quality and immune factors. Estrogen, progesterone and prolactin all have immunomodulatory effects, and prolactin can reduce the secretion of HCG in the early human placenta.
(4) Thyroid disease
Low thyroid is known to cause miscarriage and studies have found elevated antithyroid antibodies in patients with normal T3 and T4 but miscarriage. These antibodies are caused by thyroid autoimmune activation, particularly of T cells. The international consensus is that subclinical hypothyroidism is associated with recurrent miscarriages and that thyroid stimulating hormone levels need to be controlled after pregnancy. In contrast, no treatment is required for subclinical hyperthyroidism, and subclinical or satisfactorily controlled diabetes mellitus does not cause recurrent miscarriage.
3. Maternal reproductive tract abnormalities
(1) Maternal uterine anomalies
15-20% of spontaneous abortions are associated with maternal uterine anomalies. Uterine malformations include unicornuate uterus, bicornuate uterus and double uterus.
(2) Uterine adhesions
Uterine adhesions are a minor etiology for recurrent miscarriages. It is mainly caused by scraping of the uterus in consecutive recurrent miscarriages. Hysteroscopy in women with only one spontaneous miscarriage reveals that 30% of patients have uterine problems including uterine malformations and uterine adhesions, therefore, hysteroscopy is recommended in women with recurrent miscarriages.
(3) Cervical insufficiency
It is the etiology of late miscarriage and preterm delivery. If gynecologic examination reveals an open cervical opening, shortening of the cervix and dilatation of the internal diameter, urgent annulment is required.
(4) Uterine fibroids
The relationship with recurrent miscarriage is uncertain.
4. Abnormal immune function
(1) Antiphospholipid syndrome
Antiphospholipid antibodies can interfere with the formation of the placental syncytial trophoblast, leading to meconium vasculopathy, thrombosis and causing inflammatory reactions. These antibodies can lead to tissue damage, such as damage to the trophectoderm, leading to superficial attachment. Vascular endothelial damage, leading to thrombosis.
(2) Abnormalities of alloimmunity
Pregnancy can be compared to a type of semi-autograft. The antigenic portion of the male is an antigen to the mother and predisposes her to a rejection reaction. Studies have shown an association between blood NK cells and spontaneous abortion that needs to be explored.
(3) Easy embolism
This refers to a group of syndromes in which multiple coagulation mechanisms are disturbed and prone to thrombosis. Examples include deep vein thrombosis and pulmonary embolism. Pregnancy is a hypercoagulable state, and if one has a tendency to embolism, then pregnancy can easily lead to the formation of blood clots and affect the development of the fetus.
(4) Other factors
The first is male semen abnormalities, including oligospermia and sperm malformations. Studies have shown that sperm abnormalities tend to cause embryonic DNA fragmentation, but there is no conclusive evidence yet. Smoking, alcohol consumption and mental stress are also highly relevant to spontaneous abortion.